1. Field of the Invention
The present disclosure relates to a control circuit for an electric power circuit switch, and particularly, to a control circuit for an electric power circuit switch capable of reducing a control speed of a switch in response to detection of a current flowing in the electric power circuits.
2. Background of the Invention
An electric power system, which generates and consumes electric power, includes an electric power transmission network, substation, and an electric power distribution network between a power plant and consumers.
Various devices are applied to respective components of the electric power system to protect the system in the event of a fault current, and among the devices, a protective relay senses an overcurrent or a short-circuit current exceeding a normal range to drive a circuit breaker to separate a failure section from the electric power system.
When a short-circuit, or the like, occurs, very low impedance as low as line impedance of a fault spot is formed in a generator or a bus line, and thus, a very large short-circuit current flows in the electric power system (hereinafter, referred to as a ‘system’), which results in that the system suffers various problems such as a voltage drop, a frequency reduction, a thermal and mechanical stress of an electric power device, and the like, and becomes unstable. Thus, the fault section needs to be quickly separated from the electric power system in terms of stability.
In a digital protective relay, discrete Fourier transforming (abbreviated as DFT hereinafter) is commonly used to determine a fault (e.g., a fault current, such as a short-circuit, generated in a system circuit) in current of a system.
In this method, a sampled current signal flowing in a system undergoes discrete Fourier Transforming to extract a magnitude and a phase of only a frequency component of the current of the system to determine whether a fault has occurred.
Namely, only a magnitude of a frequency component is extracted from a current signal generated to have a large magnitude in the event of a fault current, and whether a current is a fault current or it has a simple surge waveform may be determined on the basis of a corresponding signal waveform.
This method is advantageous in that it is simply implemented and resistant to noise, but in case of an alternating current (AC) signal having a form such as a sine wave, input data of one period is required, so a detection time equal to or more than one period is required. Thus, in a case in which a very large fault current is generated, a load device and an electric power system are exposed to the fault current for an unnecessarily long period of time, causing a great deal of damage.